In the field of powder metallurgy, fine metal powders are compressed into the form of a workpiece in a die under high pressure. The procedure is typically carried out in huge oversized machines referred to as powder presses. In these presses, pressure is applied to the metal powder by at least one movable punch. The pressure applied to the workpiece by way of the punch, or punches, can be applied, for example, mechanically or through the use of hydraulic rams.
An example of a powder press using a hydraulic ram is shown in U.S. Pat. No. 3,788,787 to Silbereisen et al. The Silbereisen press is a powder press having a vertical orientation and upper and lower hydraulic cylinder assemblies. The upper hydraulic cylinder assembly is connected to a massive cross head, or plated. A press punch is in turn connected to the crosshead and moves downwardly into a mold cavity in the die. This action pressed the metal powder within the die to form a compressed solid workpiece having the desired height and shape. A lower punch is fixed relative to the frame.
The Silbereisen Press is representative of powder presses presently known in the art in that 1) it is designed to accommodate a variety of different workpieces by allowing for interchangeability of the tool matrix or die; 2) the distance the ram(s) travels or “stroke” is relatively fixed and, hence, it is not possible to control the position of one punch relative to another within the die; and 3) it is not possible to control a pressing force exerted by each punch to adjust for differences in punch sizes or part geometries.
In this “generic” press it is necessary to compensate for the “fixed” stroke by adapting the tool and die and appropriately connecting them to the ram(s) in order to produce a given part or workpiece. Such adaptation typically involves large structure and results in large distances between the source of force moving the ram and the actual part being produced. These large distances then translate into inaccuracies in alignment between the punches when they reach the die to form the workpiece. In addition, the powder from which the workpiece is formed is conventionally introduced to the die by a powder feed shoe that allows powder to fall gravitationally into the open upper end of the die as the feed shoe travels across the die. As the powder is compressed by the punches, density gradations in the powder create shear forces within the powder. To contain the shear forces, and other forces created by misalignment of the punches, conventional presses rely on large overall size and weight and on massive moving platens to maintain proper alignment during operation. In particular, the platens of conventional presses, and the frame members holding and guiding the platens, are also very large and very heavy in order to maintain proper alignment of the punches and the die. Because of the tremendous forces employed in the press, any misalignment can cause catastrophic failure of the press. As a result of all this required additional structure, presses of this type typically stand greater than 20 feet high and weigh more than 50 tons.
Further contributing to the massive size of conventional presses is the use of an integrated energy source. That is, each press has its own built in energy source that typically is very large considering the amount of energy needed to press a workpiece. A commercially available hydraulic automatic press known as the TPA H manufactured by Dorst Maschen and Anlagebau readily illustrates the massive size of these conventional presses. The TPA H press provides, at the lower end of the press, a first hydraulic cylinder fixed relative to the frame of the press and having a first piston that moves vertically within the first hydraulic cylinder. A second piston moves vertically within the first piston such that the first piston acts as a second hydraulic cylinder within which the second piston operates. The TPA H press also provides an upper hydraulic cylinder fixed relative to the frame of the press. The upper hydraulic cylinder has an upper piston that moves vertically relative to the upper hydraulic cylinder. Similarly to those of other conventional presses, the punches used with the TPA H press are spatially separate from the various hydraulic pistons and are held in position by large platens. Hence, this press has, as is typical with other conventional presses, a source of energy for moving the punches at a remote location from the energy, or force, receiving end of the punch. This press also has a large external frame to compensate for the shear forces on the powder and the misalignment of the punches due to large travel distances.
In order to overcome the drawbacks of conventional presses, the assignee of the present invention developed the “Hydraulic Modular Manufacturing System” described and claimed in the Related Applications referenced above. These applications describe and claim a press, press system and method for performing the pressing function of conventional presses such as powder, stamping, die casting, injection molding, etc., while, at the same time, allowing the use of a substantially smaller, lighter, portable and less expensive apparatus than conventional presses and manufacturing systems.
The manufacturing modules used in the assignee's system can be less than 1/10th the size of a conventional press. Because of its relatively small size, each manufacturing module can be manufactured to produce one specific workpiece, effectively reducing down times required to set-up conventional presses. Further, each manufacturing system can have manufacturing modules that are remote from independent power sources. This allows a number of modules to be attached to one power source, greatly conserving resources and space. The greatly reduced size, weight and complexity of a press of the present invention allows a manufacturing system to take up much less physical space than multiple conventional free standing integrated presses.
In some embodiments of the assignee's system, standard sets of presses, of sizes ranging from 120-2100 tons, may be manufactured to accept interchangeable tooling. In these systems, one hydraulic system is typically utilized per press, allowing for fast strokes for most piston motions. However, these systems still utilize a docking station where the presses are exchanged, but each docking station, or “work cell”, would have its own “independent” hydraulic system.
The assignee's press system typically includes a plurality of punches, which are preferably monolithic devices that include a work pressing end and a force-receiving end, although in some embodiments interchangeable work pressing attachments are provided at the workpiece-forming end of the punch. Because each of these punches is preferably connected to a source of hydraulic fluid, it was recognized that the force exerted by, and the position of, each of the punches may be independently controlled, either manually or via a computer. However, the unique nature of the assignee's press system created a need for a way to effectively use this ability to independently control the pressing force and punch position and to do so in a repeatable and readily adjustable manner. Further, there is a need for a way to accurately dispense precise amounts of powder in to the dies of this system. These needs are addressed by the method, control system, computer program means and article of manufacture described and claimed herein.